The present invention disclosed herein relates to a single input level shifter, and more particularly, to a single input level shifter having a single input signal and using bootstrap effect.
Recently, as a personal computer, a television, and so on become smaller, lighter, and thinner, a small, light, and thin display device is required. In order to satisfy such demands, a portable flat panel type display device using a liquid crystal display (LCD) or an organic light emitting diode (OLED) instead of a cathode ray tube (CRT) is under development. The flat panel type display device includes a thin film transistor (TFT) serving as a switching device.
In general, a voltage used for a semiconductor integrated circuit is a low voltage of less than about 5 V. However, a display device or a specific circuit uses a high voltage of more than 5 V. For example, a liquid crystal display device using a TFT may require a high voltage of about 20 V, as a pulse voltage supplied to a gate line. Accordingly, such a display device does not operate with a low voltage of less than about 5 V used for a typical semiconductor integrated circuit. Accordingly, a low voltage of less than about 5 V needs to be converted into a high voltage proper for a display device or a driving circuit for driving the same.
In order to shift low voltage into a level of high voltage proper for operations of a display device and a driving circuit, a level shifter is used. The level shifter mainly includes a single crystalline silicon wafer, an amorphous-silicon TFT, or an oxide TFT. However, when a TFT used for the level shifter has a complementary metal-oxide-semiconductor (CMOS) structure, manufacturing processes of the level shifter become complex and its manufacturing costs become high. Additionally, an oxide TFT has characteristics of a depletion mode in which threshold voltage (hereinafter, referred to be as VT) has a zero or negative value.